This invention relates to a getter assembly for use in controlling directionality of getter flash within cathode ray tubes and more particularly to a getter assembly which minimizes deposition of the getter material at undesirable locations within the cathode ray tube, such as a clear or window area.
Cathode ray tubes (CRTs) are dependent for their successful operation upon the absence of reactive gases, loose particles or other foreign material within the tube envelope. While the tube's atmosphere is evacuated prior to sealing of the tube, various residual materials, in the form of, for example, adsorbed gases or low vapor pressure solids, are released into the envelope during subsequent tube operation. In order to prevent such materials from interfering with successful tube operation, it has long been a common practice in the CRT art to deposit a "getter" material onto the interior surface of the tube envelope after it has been sealed. The function of such getter, usually barium, is to absorb the potentially harmful gases released during tube operation, and prolong the tube's useful life.
The most common means of depositing such getter material is to "flash" or evaporate it from a container located near the tube funnel interior wall by R.F. heating. Such container must be strategically shaped and placed to avoid excessive deposition in or near the neck region of the tube, since such deposition could result in stray emissions, arcing, and other operating defects, due to the low potential of the neck region of the tube compared with the higher potential region forward of the neck region. Similarly, since the getter container itself is conductive and usually supported by a conductive "wand" extending from the electron gun, excessive getter flash in the immediate vicinity of this so-called "getter assembly" must also be avoided in the interest of minimizing arcing. Finally, excessive deposition on the screen itself is obviously undesirable in that it results in reduced overall light output. However, this situation is generally uncommon in today's tube designs in which the screen is not only substantially protected from getter flash by the intervening shadow mask but also by various internal shielding means designed to shield the screen from stray electrons, and the tube itself from deleterious magnetic fields.
Various techniques have been proposed for controlling the amount and distribution of the getter flash in CRTs, with varying degrees of success. See, for example, U.S. Pat. Nos. 3,816,788 and 4,323,818.
Some recently proposed cathode ray tube applications require a clear area or window on one side of the tube funnel, and also require that the shadow mask be relatively free of getter material. No known getter assembly is capable of satisfying the above requirements while still avoiding the deposition of excessive material in the neck and getter assembly regions, needed to avoid excessive arcing.
Accordingly, it is an object of this invention to provide a getter assembly that will avoid the deposition of gettering material: (a) in a clear area or window on one side of a tube funnel; (b) in the mask area; and (c) in the neck area, yet still provide sufficient gettering material to result in useful tube operating life.